i2c: Include linux/of.h header

'of_match_ptr' is defined in linux/of.h. Include it explicitly to
avoid build breakage in the future.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/busses/i2c-pnx.c

@@ -23,6 +23,7 @@
 #include <linux/err.h>
 #include <linux/clk.h>
 #include <linux/slab.h>
+#include <linux/of.h>
 
 #define I2C_PNX_TIMEOUT_DEFAULT		10 /* msec */
 #define I2C_PNX_SPEED_KHZ_DEFAULT	100